Problem: Simplify the following expression: ${-8n+12-6n+9}$
Explanation: Rewrite the expression to group the ${n}$ terms and numeric terms: $ {-8n - 6n} + {12 + 9}$ Combine the ${n}$ terms: $ {-14n} + {12 + 9}$ Combine the numeric terms: $ {-14n} + {21}$ The simplified expression is $-14n+21$